We evaluate a decadal ozone profile record derived from the Suomi National Polar-orbiting Partnership (SNPP) Ozone Mapping and Profiler Suite (OMPS) Limb Profiler (LP) satellite instrument. In 2023, the OMPS LP data were re-processed with the new version 2.6 retrieval algorithm that combines measurements from the ultraviolet (UV) and visible (VIS) parts of the spectra and employs the second order Tikhonov regularization to retrieve a single vertical ozone profile between 12.5 km (or cloud tops) and 57.5 km with the vertical resolution of about 1.9 - 2.5 km between 20-55 km. The algorithm uses radiances measured at six UV ozone-sensitive wavelengths (295, 302, 306, 312, 317 and 322 nm) paired with 353 nm, and one VIS wavelength at 606 nm combined with 510 nm and 675 nm to form a triplet. Each wavelength pair or triplet is used over a limited range of tangent altitudes where the sensitivity to ozone changes are strongest. A new implemented aerosol correction scheme is based on a gamma-function particle size distribution. Numerous calibration changes that affected ozone retrievals were also applied to measured LP radiances, including updates in altitude registration, radiometric calibration, stray light, and spectral registration. The key version 2.6 improvement is the reduction in relative drifts between LP ozone and correlative measurements, linked previously to a drift in the version 2.5 LP altitude registration. We compare LP ozone profiles with those from Aura Microwave Limb Sensor (MLS) to quantify ozone changes in version 2.6.

Understanding lowermost stratosphere (LMS) ozone variability is an important topic in the trends and climate assessment communities because of feedbacks among changing temperature, dynamics and ozone. LMS evaluations are usually based on satellite observations. Free tropospheric (FT) ozone assessments typically rely on profiles from commercial aircraft. Ozonesonde measurements constitute an independent dataset encompassing both LMS and FT. We used Southern Hemisphere Additional Ozonesondes (SHADOZ) data (5.8°N to 14°S) from 1998-2019 in the Goddard Multiple Linear Regression model to analyze monthly mean FT and LMS ozone changes across five well-distributed tropical sites. Our findings: (1) both FT (5-15 km) and LMS (15-20 km) ozone trends show marked seasonal variability. (2) All stations exhibit FT ozone increases in February-May (up to 15%/decade) when the frequency of convectively-driven waves have changed. (3) After May, monthly ozone changes are both positive and negative, leading to mean trends of +(1-4)%/decade, depending on station. (4) LMS ozone losses reach (4-9)%/decade mid-year, correlating with an increase in TH as derived from SHADOZ radiosonde data. (5) When the upper FT and LMS are defined by tropopause-relative coordinates, the LMS ozone trends all become insignificant. Thus, the 20-year decline in tropical LMS ozone reported in recent satellite-based studies likely signifies a perturbed tropopause rather than chemical depletion. The SHADOZ-derived ozone changes highlight regional and seasonal variability across the tropics and define a new reference for evaluating changes derived from models and satellite products over the 1998 to 2019 period.

Quantifying variability in the lowermost stratosphere (LMS) is important because of feedbacks among changing temperature, dynamics and species like ozone. We used reprocessed Southern Hemisphere Additional Ozonesondes data from 1998-2018 in a Multiple Linear Regression (MLR) model to analyze variability and trends in free tropospheric (FT) and LMS ozoneacross five well-distributed tropical regions. The MLR also computed trends in a proxy for convection as determined from laminae in each ozonesonde-radiosonde pair. Only the equatorial Americas exhibits statistically significant annual trends in FT or LMS ozone. At the other sites, ozonetrends occur in isolated layers during months when convection has changed, February-April or July-November. Our results imply that large FT ozone increases reported for populated tropical areas may be caused by growing pollution overlying smaller changes caused by perturbed dynamics. They also provide regional data for evaluating LMS ozonetrends based on zonal averages of often sparse satellite measurements

In this study, we present evaluation of version 3 ozone products derived from the DSCOVR EPIC instrument. EPIC’s total and tropospheric ozone columns have been compared with correlative satellite and ground-based measurements at time scales from daily averages to monthly means. We found that the agreement improves if we only accept retrievals derived from the EPIC 317 nm triplet and limit solar zenith and satellite looking angles to 70°. With such filtering in place, the comparisons of EPIC total columns with correlative satellite and ground-based data show mean differences within ±5-7 DU (or 1.5-2.5%). The biases with OMI and OMPS NM tend to be mostly negative in the Southern Hemisphere (SH), while there are no clear latitudinal patterns in ground-based comparisons. Evaluation of the EPIC ozone time series at different ground-based stations with the correlative ground-based Brewer and Pandora instruments and ozonesondes demonstrated good consistency in capturing ozone variations at daily, weekly and monthly scales with a persistently high correlation (r2>0.9) for total and tropospheric columns. We examined the quality of EPIC tropospheric ozone columns by comparing with ozonesondes at 12 stations and found that differences in tropospheric column ozone are within ±2.5 DU (or ~±10%) after removing a constant 3 DU offset at all stations between EPIC and sondes. The analysis of the time series of zonally averaged EPIC tropospheric ozone revealed a statistically significant drop of ~2-4 DU (~5-10%) over the entire NH in spring and summer of 2020, which is partially related to the unprecedented Arctic stratospheric ozone losses in winter-spring 2019/2020 and reductions in ozone precursor pollutants due to the COVID-19 pandemic.